Intel's plan to ship a Pentium 4 Extreme Edition with 2MB of in-core L2 cache - as opposed to 2MB of on-chip L3 cache - is to be followed up by a version pitched at mainstream desktops.

So claims Japanese-language website PC Watch, which suggests this Pentium 4 6xx series will debut early next year.

The 3.73GHz P4EE is currently believed to be scheduled for late Q4 2004 availability. The chip will be the first 90nm P4EE, and the first to be based on Pentium 4 technology rather than Xeon chips. It will also be the first P4EE to carry a model number, shipping as a 7xx series desktop part.

Earlier this year, the part's appearance on Intel roadmaps caused much confusion, since it was assumed that the 7xx series referred to the 90nm 'Dothan' Pentium M family. To be fair, Intel always said that the P4EE desktop chips would eventually ship as 7xx parts, but we and plenty of other Intel watchers forgot.

But back to the 6xx series. According to the Japanese site's report, it will debut in Q1 2005, in four incarnations clocked to 3.2GHz, 3.4GHz, 3.6GHz and 3.8GHz, dubbed the 640, 650, 660 and 670, respectively.

Interestingly, the long-awaited 4GHz P4, also due in Q1 2005, after Intel delayed it, will ship as the 580. The 6xx series' extra cache therefore neatly allows Intel to offer higher-performing processors without having to up - quite the reverse, in fact - the clock frequency beyond 4GHz.

So far, it CPU numbering scheme has largely kept in sync with clock speed advances, but with the 6xx series the two finally separate, and for Intel the megahertz myth is at last put to rest.

The introduction of the 6xx series begs one further question: if the 6xx is essentially the same chip as the P4EE, what is justifying the 7xx classification over the 6xx? The answer appears to be the 1066MHz frontside bus: the 6xx series will support an 800MHz FSB, with the higher-speed bus not being brought to the P4 line until next Summer's dual-core 'Smithfield' release. ®